Problem with gfortran and snowleopard

Hi guys,
I know this post is quite similar to this one so I apologize in advance in case I cause any irritation. Unfortunately I have to compile an f.77 code on my snowleopard and try writing a mixed language code using fortran and C++. this is part of the research in our team and I am still bumping heads with the other guys on writing programs in C++. anyways, I have donwloaded the .dmg file from GCC's website that is supposed to instal gfortran 4.5.0 for snowleopard. but when I type gfortran in the terminal just to check whether the compiler has been installed correctly I get :

I am using eclipse helios with photran but the same error pops up when I try compiling the code in the terminal. Anyways, It indicates that Im having some incompatibilities compiling the code for 64bit.

so, any ideas on how to fix this? I really hate working with fortran I just hope I get this over with soon

Now I believe the problem is with my current version of GCC. Since I am using apple's 4.2.1. Maybe I should install the new version? I just fear that by installing the new version I might blow something up :-s

thanks alot B, I got everything under control. I only have one question, I used the export PATH command to change the default compiler of the system. Now whenever I type GCC -v the terminal uses 4.6.0. Should I use the export command again in case I needed to use the previous GCC 4.2.1?

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